Figure 4. Flexion-extension lateral radiographs demonstrating instability.
If spondylolysis is suspected but not demonstrated on plain films, oblique linear tomography and CT will clearly show the defect (Fig.5).49 In the early acute stages, radio nuclide scanning with single-photon emission computed tomography (SPECT) pinhole imaging is much more sensitive than plain radiographs (Fig. 6).14 This is of great practical significance in that fresh pars defects may heal with early effective immobilization.
Magnetic resonance imaging, myelography, myelo-CT scanning, and discography are of occasional use (Fig. 7). Such studies are more commonly obtained in older individuals to rule out associated disc herniations and to assess the integrity of motion segments adjacent to a proposed fusion. Even in adolescents, MRI scanning and discography demonstrated disc degeneration to be the rule below the olisthetic vertebra and to be quite common above it.39 At this point, the implications of this knowledge remain unclear. (See the article by Greenan in this issue for a detailed discussion of radiologic assessment of the athlete's spine.)
NATURAL HISTORY
In the management of the athlete with a symptomatic pars defect, it is important to identify risk factors that may increase the likelihood of progressive deformity or back pain in the future. Several authors have followed the clinical course and have looked for clinical and radiographic signs of prognostic value for progression and functional